In building computer systems it is common place to interface various computer components, such as one computer to another, and/or various peripheral equipment to a computer. This interfacing is accomplished by an intermediary electronic circuit which is generically referred to as interfacing equipment.
A special problem exists in interfacing logic circuitry of the newer computers with logic circuitry of the computers of the 1960 era. The newer microelectric logic circuitry normally operates between ground and a power supply voltage of +5 volts, and the logical levels are nominally +0.2 volts for a 0 and +3.3 volts for a 1. This is in contrast to the 1960 era discrete component logic circuits where logic levels are typically -0.1 volts for a 0 and -3.2 volts for a 1. In the past the method for interfacing these newer and older circuits has consisted of an intermediary electronics circuit called a level shifter. A lever shifter consists of discrete components, such as several transistors, resistors, etc. which require considerable additional power and space. Further disadvantages are that the impedance levels are usually high so that the circuits are susceptible to noise and additional propagation delays are introduced.